The demand for smaller and lighter devices used in wireless communications (e.g., cellphones) continues. Often, this means that the size of batteries incorporated in these devices is also desirably smaller. Concomitantly, the desired duration of active use of the wireless device, without interruption for recharging, is increasing. As such, it is desired to provide power to the device over a longer duration with a battery of reduced size
In a device for wireless communication, a radio frequency (RF) power amplifier drains most of the power consumed by the device. For this reason, much effort has been given to enhancing the efficiency of the RF power amplifier. As a result, multiple mode power amplifiers have been developed.
In a multiple mode power amplifier, it is possible to switch between a high power mode and a low power mode. For example, when the device is located at a comparatively large distance from a base station the multimode power amplifier operates in high power mode; and when the device is located at a comparatively short distance from a base station, the multimode power amplifier operates in low power mode. In a known multiple mode power amplifier the switching between high power mode and low power mode is effected with an RF switch.
However, the incorporation of an RF switch into the power amplifier of a device for wireless communications adds to the overall cost of the device. Further, RF switches have a negative gain, which may reduce the overall efficiency of the power amplifier. Accordingly, there is a need to provide a power amplifier that does not require an RF switch.
However, there are drawbacks to known multiple mode power amplifiers that do not include an RF switch. For example in certain known multiple mode power amplifiers, when operating in the high power mode, an RF signal is transferred to two amplifying stages. The two signals amplified by the respective stages have different phases. As such, when they are superimposed together at an output, a power loss may take place due to a phase difference therebetween, causing a decrease in the efficiency of the multiple mode power amplifier. Moreover, when the known multiple mode power amplifier operates in the low power mode, it is required to flow a low output current at an output port of a second amplifying stage in order to reduce the power consumption of the multiple mode power amplifier. In order to reduce the output current, an inductor of a comparatively high inductance (e.g., from about 2 to 4 nH) is used in an impedance matching network at the output of the second amplifying stage. However, in order to have such high inductance, the size of an inductor (and, therefore, a power amplifier employing such inductor) must be comparatively large. Ultimately, the goal of providing a wireless communication device of reduced size is compromised.